#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include <iomanip>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=1e5+100;
typedef long long LL;
const double pi=acos(-1);
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[maxn],b[maxn],dp[maxn];
struct Tree{
    LL l,r,maxval;
}tree[maxn*4];
void push_up(LL p){
     tree[p].maxval=max(tree[p*2].maxval,tree[p*2+1].maxval);
}
void build(LL p,LL l,LL r){
     tree[p].maxval=0;tree[p].l=l;tree[p].r=r;
     if(l==r){return;}
     LL mid=(l+r)>>1;
     build(p*2,l,mid);build(p*2+1,mid+1,r);
     push_up(p);
}
void modify(LL p,LL l,LL r,LL d){
     if(l<=tree[p].l&&r>=tree[p].r){
            tree[p].maxval=d;
            return;
     }
     LL mid=(tree[p].l+tree[p].r)>>1;
     if(l<=mid) modify(p*2,l,r,d);
     if(r>mid) modify(p*2+1,l,r,d);
     push_up(p);
}
LL query(LL p,LL l,LL r){
     if(l<=tree[p].l&&r>=tree[p].r){
        return tree[p].maxval;
     }
     LL mid=(tree[p].l+tree[p].r)>>1;
     LL ans=0;
     if(l<=mid) ans=max(ans,query(p*2,l,r));
     if(r>mid) ans=max(ans,query(p*2+1,l,r));
     return ans;
}
int main(void){
        cin.tie(0);std::ios::sync_with_stdio(false);
        LL n;cin>>n;
        for(LL i=1;i<=n;i++){
            LL r,h;cin>>r>>h;
            a[i]=r*r*h;b[i]=a[i];
        }
        sort(b+1,b+1+n);
        build(1,1,n);
        LL ans=0;
        for(LL i=1;i<=n;i++){
            LL tmp=lower_bound(b+1,b+1+n,a[i])-b;
            dp[i]=max(dp[i],query(1,1,tmp-1)+a[i]);
            modify(1,tmp,tmp,dp[i]);
            ans=max(ans,dp[i]);
        }
        cout<<fixed<<setprecision(10)<<(1.0*ans*pi) <<"\n";
        return 0;
}
